The present invention relates to an actuator mechanism for a pump, and in particular, to an improved actuator mechanism for use in an internally implantable blood pump or the like.
A variety of different types of heart replacement and heart-assist pumps have been proposed in the prior art. One type of pump which offers advantages in size, weight and reliability is a so-called deformable-sac pump, in which a pair of opposed pusher plates are movable reciprocally from relatively more displaced positions to relatively less displaced positions for expelling the fluid contents of a deformable sac. By way of example, a pump of this general type is shown and described in U.S. Pat. No. 4,167,046. Briefly the device described therein includes a disk-like deformable sac having an annular side wall supported in a rigid condition and a pair of opposed movable walls against which the reciprocally movable pusher elements act. Various advantages inherent in this construction are set forth in the aforementioned patent.
The actuator which is used in a deformable-sac pump of the type just described operates to move the opposed pusher plates recurrently from their more displaced to their less displaced positions, preferably in a manner which produces controlled-rate, synchronous plate movement. At the same time, the actuator must be efficient, relatively smooth working, and reliable over long periods of continued use. One type of actuator which provides a number of advantages in a deformable-blood sac has been described in U.S. patent application for Pump and Actuator Mechanism, Ser. No. 211,210, filed Nov. 28, 1980, and assigned to the assignee of the present application.
The actuator disclosed in the just-mentioned application includes a solenoid device which operates between open and closed positions to produce increased bending in opposed prestressed beam springs which operatively connect opposed armatures in the actuator to associated pusher plates. The increased bending in the springs is released by movement of the two pusher plates inwardly toward their less displaced end-of-stroke positions. An important feature of the actuator is that the beam springs, in acting between less stressed and more stressed conditions, produce a relatively flat output force profile in acting against the associated pusher plates. As a result, peak loads on the pump components are minimized. The actuator, having few moving parts, is also simple in construction and operation, and is therefore quite reliable over long periods of continued use.
The present invention contemplates an improved actuator which incorporates many of the advantageous features of the actuator just described, and further includes a number of unique and hitherto unknown features which enhance pump reliability and operational characteristics and contribute to compactness in the pump design.
Accordingly, one object of the present invention is to provide an actuator for use in a deformable-sac type implantable blood pump, where the actuator is quite compact.
Another object of the invention is to provide such an actuator having highly reliable and predictable performance characteristics.
It is yet another object of the invention to provide such an actuator whose operation can be accurately monitored and controlled.
The actuator of the invention includes an armature which is mounted for movement between open and closed positions, and which includes a solenoid core defining an internal front-to-back slots. An elongate main spring in the actuator is attached at one spring end to the back region of the armature, extends through the core slot, and is attached at its other end to a pusher element adapted to act against a deformable sac. An elongate preload spring connected at one of its ends to the armature and operatively connected at its other end to the main spring functions to support the main spring in a relatively less stressed condition when the armature is in its open position.
In a preferred embodiment of the invention, the main spring includes a plate-like spring which is curved in the direction of its action on the pusher element, and is in a more planar configuration when in its relatively more stressed condition.
Also in a preferred embodiment of the invention, the actuator includes a symmetrical arrangement of components acting on opposed pusher elements to compress the sac symetrically from opposite sides. The actuator may further include position sensors for monitoring solenoid armature and/or main spring positions, to provide data used in controlling the operation of the actuator.